Desiccant dehumidification system and method

ABSTRACT

A system and method for controlling the humidity of an indoor space is disclosed. The system features a desiccant wheel which rotates sequentially through a plurality of distinct process air streams in order to optimize desiccant moisture adsorption at the process side of the desiccant wheel. This moisture is then deposited on the regeneration side of the wheel upstream of a cooling coil, increasing the dew point of the air entering the coil. The latent capacity and operational temperature of the coiling coil will be increased as a result, thus enhancing the dehumidification performance of the cooling coil and the overall efficiency of the system.

This application is a divisional application of U.S. patent applicationSer. No. 13/715,849, filed on Dec. 14, 2012 now U.S. Pat. No. 8,828,128,which claims the benefit of U.S. Provisional Application No. 61/580,149,filed on Dec. 23, 2011, both of which are hereby incorporated byreference in their entirety.

BACKGROUND

Insufficient dehumidification in indoor facilities can lead to thedeterioration of building materials as well as cause seriousmoisture-related health issues. Conventional HVAC systems utilizemechanical refrigeration to achieve both sensible and latent cooling.Latent cooling (i.e., dehumidification) occurs when the air is passedover a cooling coil, thereby lowering the air temperature below theentering dew point and causing a portion of the moisture in the air tocondense on the coil's surface and drop out of the airflow.

Mechanical refrigerative dehumidification is most effective when the airis at higher temperatures and the relative humidity approaches 100%.However, the latent cooling efficiency of mechanical refrigerationdiminishes in low relative humidity environments. In such dryconditions, the air temperature must be cooled below the entering dewpoint in order to remove moisture from the air. The resulting cold airthen must be reheated to avoid over-cooling the space, therebyincreasing energy use. Additionally, in subfreezing dew pointapplications such as ice rink arenas, periodic defrosting cycles arenecessary due to ice accumulation on the cooling coils.

Desiccant wheels have been incorporated into air handling systems toreplace or enhance the dehumidification performance of mechanicalrefrigerative dehumidification. Unlike mechanical refrigeration whichrelies upon cooling the air below its dew point, desiccantdehumidification relies on adsorption. Moisture transfer by thedesiccant is driven by the difference in relative humidity of the“process” and “regeneration” air streams. When the relative humidity ofthe regeneration air stream is lower than the relative humidity of theprocess air stream, the desiccant will adsorb moisture from the processair stream and transfer it to the regeneration air stream.

Desiccant dehumidification systems are typically designed in eitherdual-path or single-path configurations depending on the application. Aschematic illustration of a conventional dual-path desiccantdehumidification system is shown in FIG. 1. In the dual-pathconfiguration, two counter-current air streams power the operation ofthe desiccant dehumidification system. The desiccant wheel rotatesthrough these two air streams and transfers moisture from the higherrelative humidity process air stream to the lower relative humidityregeneration air stream. Because the relative humidity of the airleaving the process side of the wheel can only get as low as therelative humidity of the air entering the regeneration side of thewheel, a heat source is typically utilized to heat the regeneration airstream to lower its relative humidity. Typical heat sources includedirect-fired gas heaters, electric heaters, and indirect heat sourcessuch as steam, hot water, solar, and waste heat from the building.Depending on the targeted indoor conditions, regeneration airtemperatures usually range from 100° F. to 300° F., which in turn raisesthe dry-bulb temperature of the process air leaving the desiccant wheel.Accordingly, most dual-path systems include a cooling coil downstream ofthe process side of the wheel to re-cool the air before supplying it tothe conditioned space.

A schematic illustration of a conventional single-path desiccantdehumidification system is shown in FIG. 2. These systems are sometimesreferred to as “Cromer Cycle” systems. Single-path desiccantdehumidification systems are designed to enhance the dehumidificationperformance of a traditional cooling coil in applications which wouldotherwise be difficult and expensive to maintain using mechanicalrefrigeration alone. In such systems, moisture transfer occurs within asingle air stream. The desiccant wheel is configured in series with acooling coil such that the regeneration side of the wheel is locatedupstream of the coil and the process side of the wheel is locateddownstream of the coil. The air downstream of the cooling coil will beat a very high relative humidity as it enters the process side of thedesiccant wheel. The desiccant wheel will adsorb moisture from thesaturated air downstream of the coil and deposit it back into the airupstream of the coil. This moisture will then be removed from the air bythe coil via condensation. The addition of the desiccant wheel to theconventional mechanical refrigeration system enhances thedehumidification performance of the traditional cooling coil byincreasing the latent capacity of the cooling coil without increasingits total cooling capacity. And, unlike a conventional mechanicalrefrigeration system with a cooling coil alone, the supply air dew pointcan be lower than the coil surface temperature.

In certain applications, single-path desiccant dehumidification systemsare capable of providing significant energy savings over dual-pathdesiccant dehumidification systems. Unlike dual-path systems,single-path systems typically do not require an external heat source toregenerate the desiccant wheel. Further, post-cooling may not benecessary with single-path systems, whereas the process air stream indual-path systems oftentimes must be re-cooled before it's supplied tothe conditioned space.

A shortcoming of current-generation single-path desiccant systems,however, is the inability to drastically reduce moisture content fromthe processed air. Further, the effectiveness of current generationsingle-path systems is significantly diminished in applications wherethe air entering the system has a high relative humidity. This is onlyexacerbated where the incoming air has a low temperature in addition tohigh relative humidity. In such conditions, periodic defrosting cyclesmay be necessary due to frost buildup on the coils. As a result,dual-path systems are still predominately used in low dew pointapplications such as ice rink arenas despite their high energy usage perpound of water removed.

SUMMARY

A system and method for controlling the humidity of an indoor space isdescribed herein. The system features a desiccant wheel which rotatessequentially through a plurality of distinct process air streams inorder to optimize desiccant moisture adsorption at the process side ofthe wheel. The rotation of the desiccant wheel sequentially through theplurality of distinct process air streams allows the system toefficiently produce supply air having a lower relative humidity thanthat achievable by conventional single-path desiccant wheel systems. Thesystem is also capable of maintaining a higher operational cooling coiltemperature due to the increased latent load supplied at the coolingcoil. This not only improves the COP (coefficient of performance) of thesystem's refrigeration system, but also eliminates the need for defrostcycles (and the accompanying defrost cycle components) in subfreezingdew point applications. Furthermore, because the system allows theentire latent load to be decoupled from the building's conventionalcooling system, the conventional cooling system can be downsized tohandle only the sensible load of the building.

The above summary is not intended to describe each illustratedembodiment or every possible implementation. These and other features,aspects, and advantages of the present invention will become betterunderstood with regard to the following description, appended claims,and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional dual-path desiccantdehumidification system.

FIG. 2 is a schematic view of a conventional single-path desiccantdehumidification system.

FIG. 3 is a schematic view of an embodiment of the dehumidificationsystem of the present invention.

FIG. 4a is a front perspective view of an exemplary desiccant wheel unitwhich may be utilized in the present invention.

FIG. 4b is a rear perspective view of an exemplary desiccant wheel unitwhich may be utilized in the present invention.

FIG. 5a is a schematic view of an alternative embodiment of thedehumidification system of the present invention.

FIG. 5b is a psychrometric chart showing the performance of thedehumidification system depicted in FIG. 5 a.

FIG. 6 is a front perspective view of an embodiment of andehumidification system of the present invention.

FIG. 7 is a right side view of the dehumidification system depicted inFIG. 6.

FIG. 8 is a top view of the dehumidification system depicted in FIG. 6.

FIG. 9 is a rear perspective view of the dehumidification systemdepicted in FIG. 6.

FIG. 10 is a left side perspective view of the dehumidification systemdepicted in FIG. 6.

FIG. 11 is a schematic view of an alternative embodiment of thedehumidification system of the present invention.

FIG. 12a is a schematic view of an alternative embodiment of thedehumidification system of the present invention.

FIG. 12b is a psychrometric chart showing the performance of thedehumidification system depicted in FIG. 12 a.

FIG. 13a is a schematic view of an alternative embodiment of thedehumidification system of the present invention.

FIG. 13b is a psychrometric chart showing the performance of thedehumidification system depicted in FIG. 13 a.

FIG. 14 is a schematic view of an alternative embodiment of thedehumidification system of the present invention,

DESCRIPTION

The description which follows, and the embodiments described therein, isprovided by way of illustration of examples of particular embodiments ofprinciples and aspects of the present invention. These examples areprovided for the purposes of explanation—and not of limitation—of thoseprinciples of the invention. In the description that follows, like partsare marked throughout the specification and the drawings with the samerespective reference numerals.

A system embodying features of the present invention is shownschematically in FIG. 3. The system 100 comprises an means for creatinga first air stream 101 and a second air stream 102 (e.g., an airsupplier 150); a heating means 110 positioned within the second airstream 102 for heating the air; a cooling means 130 positioned withinthe second air stream 102 for cooling and dehumidifying the second airstream 102; a desiccant wheel unit 120 having its regeneration sidepositioned in the second air stream 102 between the heating means 110and the cooling means 130 and having its process side positionedpartially in the second air stream 102 and partially in the first airstream 101 in order to allow the desiccant wheel system 120 to transfermoisture from the first air stream 101 and the process portion (i.e.,the portion between Points D-E) of the second air stream 102 into theregeneration portion (i.e., the portion between Points A-C) of thesecond air stream 102.

The heating means 110 can comprise any means capable of raising thedry-bulb temperature of the air entering the system, including but notlimited to direct heat sources (e.g., gas or electric heaters) orindirect heat sources (e.g., steam, hot water, solar, and waste heatfrom the building). The cooling means 130 can comprise chilled water,cooling coils, or any other means capable of dehumidifying a passing airstream. In a preferred embodiment described below, a vapor-compressionrefrigeration system (DX system) is utilized, with the condenser servingas the heating means 110 and the evaporator coil serving as the coolingmeans 130.

The means for creating the first air stream 101 and the second airstream 102 can be one or more air suppliers 150 such as fans, blowers,or any other means capable of moving air so as to create an air stream.In the embodiment depicted in FIG. 3, the air supplier 150 is shownpositioned along the supply passageway 190. This positioning allows asingle air supplier 150 to be used to create both the first and secondair streams 101, 102. However, in alternative embodiments, a first airsupplier 150 can be positioned in the cycle passageway 180 and a secondair supplier 150 can be positioned in either the bypass passageway 170or the supply passageway 190. The air supplier(s) may be located withinthe system itself or can be positioned externally to the system andconnected by ductwork. The first and second air streams 101, 102 cancomprise return air (i.e., air drawn from the conditioned space),outdoor air (i.e., air drawn from the atmosphere), or a mixture ofreturn air and outside air.

The desiccant wheel unit 120 preferably comprises a rotating desiccantwheel 121 rotatably mounted within a cassette cabinet 122 (See FIGS. 4aand 4b ). Preferably, the cassette cabinet 122 is partitioned into threesections to define a regeneration section and two process sections ofthe desiccant wheel 121. The “regeneration side” or “regenerationsection” of the desiccant wheel 121 is that portion of the wheel whichis exposed to passing air at the regeneration inlet 125 of the cassettecabinet 122. The “first process section” of the desiccant wheel 121 isthat portion of the wheel 121 which is exposed to passing air at thefirst process inlet 127 of the cassette cabinet 122. The “second processsection” of the desiccant wheel 121 is that portion of the wheel 121which is exposed to passing air at the first second inlet 129 of thecassette cabinet 122. Collectively, the first and second processsections comprise the “process side” of the desiccant wheel 121. Theregeneration inlet 125 and process inlets 127, 129 of the cassettecabinet 122 can be of varying proportions depending on the application.

The system 100 is configured to transmit two separate air streamsthrough the first and second process inlets 127, 129 of the cassettecabinet 122 so as to allow for sequential adsorption of moisture by theexposed portions of the desiccant wheel 121. The first air stream 101can be transmitted through a bypass passageway 170, while the second airstream 102 can be transmitted through a cycle passageway 180. The bypasspassageway 170 and the cycle passageway 180 are separated by a partition(not shown) so that the first and second air streams 101, 102 do not mixprior to entering the process side of the desiccant wheel 121. Thispartition may comprise discrete plenums, ducts, or a baffle between thetwo air streams. Further, the cycle passageway 180 itself may besubdivided into a heating plenum in fluid communication with a coolingplenum. Dampers can be utilized at the inlets 171, 181 of the bypass andcycle passageways to modulate flow through the system 100.

In operation, first and second air streams 101, 102 are drawn into thebypass and cycle passageways 170, 180, respectively, by the air supplier150. The first air stream 101 enters the inlet 171 of the bypasspassageway 170 and then passes through the exposed portion of thedesiccant wheel 121 at the first process inlet 127. Meanwhile, thesecond air stream 102 enters the inlet 181 of the cycle passageway 180and is heated by the heating means 110, thereby lowering the air'srelative humidity. The hot, dry air then passes through the exposedportion of the desiccant wheel 121 at the regeneration inlet 125,regenerating (i.e., drying) the wheel 121. The second air stream 102will leave the regeneration section of the wheel 121 cooled andsaturated. Next, the second air stream 102 passes through the coolingmeans 130 where it is cooled to its dew point to remove moisture viacondensation. The cooled saturated air is then passed through theexposed portion of the desiccant wheel 121 at the second process inlet129 where the air is heated and dried. The dehumidified first and secondair streams 101, 102 are then mixed in the supply passageway 190 beforeexiting the outlet 191.

The desiccant wheel 121 is configured to rotate in a direction to allowthe freshly regenerated section of the wheel 121 to first come intocontact with the first air stream 101 before rotating into contact withthe process portion of the second air stream 102. Rotating the freshlyregenerated section of the wheel 121 sequentially through the first andsecond air streams 101, 102 provides two significant advantages overcurrent generation single-path desiccant dehumidification systems.

Firstly, the sequential adsorption technique optimizes desiccantmoisture adsorption at the process side of the wheel 121. The second airstream 102 will have a relative humidity nearing 100% after it exits thecooling means 130. Therefore, the process portion of the second airstream 102 typically will have a higher relative humidity than the firstair stream 101 at the process side of the desiccant wheel 121. Becausethe desiccant only adsorbs moisture when the surface vapor pressure islower than that of the passing air, it is necessary for the freshlyregenerated section of the wheel 121 to first come into contact withlower relative humidity air stream (the first air stream 101) beforerotating into contact with the saturated air stream (second air stream102). In this configuration, maximum moisture adsorption will beachieved resulting in more water being available for removal at theregeneration side of the desiccant wheel 121. The increased availabilityof moisture for removal at the regeneration side of the wheel 121 willtrade sensible capacity for additional latent capacity, thereby loweringthe sensible-to-latent heat ratio of the system 100.

Secondly, the sequential adsorption technique allows the first airstream 101 to function as a heat sink thereby removing excess heatenergy from the cycle passageway 180. Further, this allows theadsorption process from the second air stream 102 to be more adiabaticin nature, thus further increasing the overall moisture adsorption bythe desiccant wheel at the process side.

A preferred embodiment of the system 100 of the present invention isshown schematically in FIG. 5a . In this embodiment, a mechanicalrefrigeration system is utilized, with the condenser serving as theheating means 110 and the evaporator coil serving as the cooling means130. The refrigerant cooling system includes a compressor 240 for theliquid/gas refrigerant which is carried in refrigerant lines 241 betweena condenser coil 210 and an evaporator coil 230. The compressor 240preferably is a variable capacity compressor.

By utilizing the waste heat off of the condenser 210 as the heatingmeans used to regenerate the desiccant wheel 121, the efficiency of thesystem 100 can be optimized. Normally, the placement of a condenserupstream of an evaporator coil in a closed thermodynamic system wouldcause excess energy to build up in the refrigeration loop, ultimatelyresulting in the system overheating and failing. However, because thedesiccant wheel 121 rotates first through the first air stream 101 andthen through the second air stream 102, the first air stream 101functions as a heat sink allowing excess energy to be removed from therefrigeration loop (the cycle passageway 180) by the first air stream101.

Rotating the freshly regenerated section of the wheel 121 sequentiallythrough the first and second air streams 101, 102 allows the system 100to efficiently produce supply air having a lower relative humidity thanthat achievable by conventional single-path desiccant wheel systems. Thesystem is also capable of maintaining a higher operational cooling coiltemperature due to the increased latent load supplied at the evaporatorcoil. This not only improves the COP (coefficient of performance) of thesystem's refrigeration system, but also eliminates the need for defrostcycles (and the accompanying defrost cycle components) in subfreezingdew point applications. Furthermore, because the system allows theentire latent load to be decoupled from the building's conventionalcooling system, the conventional cooling system can be downsized tohandle only the sensible load of the building.

An embodiment of a dehumidification system exemplifying features of thepresent invention is shown in FIGS. 6-10. The dehumidification system200 comprises an enclosure 201 divided into plenum sections 202 h, 202c, 202 b, and 202 s by the vertical wall 205 and the intermediateceiling 207. The compressor 240 and condenser coil 210 are located inheating plenum 202 h adjacent to the regeneration section of thedesiccant wheel 121. The evaporator coil 230 is located in coolingplenum 202 c downstream from the regeneration side of the desiccantwheel 121 and upstream from the second process section of the desiccantwheel 121. The air supplier 150 is located in plenum 202 s downstreamfrom the process side of the desiccant wheel 121. In this particularconfiguration, the desiccant wheel is designed to rotate clockwiserelative to the front side of the dehumidification system 200 to allowthe freshly regenerated portion of the wheel 121 to first come intocontact with the first air stream 101 before rotating into contact withthe second air stream 102. The front side of the dehumidification system200 is demarcated in FIG. 6 with the reference character “X.”

In operation, first and second air streams 101, 102 are drawn into theplenum sections 202 h and 202 b by the air supplier 150. The first airstream 101 flows through plenum 202 b, through the first process inlet127, and then through the first process section of the desiccant wheel121. Meanwhile, the second air stream 102 flows over the condenser coil210 located in plenum 202 c, heating the second air stream 102 andlowering its relative humidity. The hot, dry air then passes through theregeneration inlet 125 of the cassette cabinet 122, regenerating (i.e.,drying) the exposed portion of the wheel 121 while humidifying andcooling the air. Next, the humidified cooled second air stream 102enters the plenum 202 c and passes through the evaporator coil 230 whereit is cooled to its dew point to remove moisture via condensation. Thesecond air stream 102—which now consists of cooled, saturated air—isthen passed through the second process inlet 129 into the exposedportion of the desiccant wheel 121, heating and further dehumidifyingthe air. The dehumidified first and second air streams 101, 102 are thenmixed in the plenum 202 s before exiting the unit 200.

An alternative embodiment of a dehumidification system having featuresof the present invention is shown schematically in FIG. 11. In thisembodiment, a mechanical refrigeration system is utilized in a similarmanner to the embodiment depicted in FIG. 5 a. However, in thisembodiment, a second external, condenser 211 has been added to therefrigeration circuit in order to remove excess heat from therefrigeration loop.

Another alternative embodiment of the present invention is shown in FIG.12a . In this embodiment, the system 300 is configured to introduce amixture of return air and outside air to the conditioned space toaddress ventilation requirements of the space. Depending on the targetedparameters for the conditioned space and the enthalpy of the outdoorair, it may be necessary to pretreat the outdoor air before transmittingit through the process side of the desiccant wheel 121. In theembodiment depicted in FIG. 12a , a separate refrigeration circuit isutilized to lower the enthalpy of the outdoor air as needed. Therefrigeration circuit comprises an evaporator 330, an external condenser310, and a compressor 340. The performance results of the system areshown in the psychrometric chart depicted in FIG. 12 b.

Another alternative embodiment configured for processing outdoor air isdepicted in FIG. 13a . In this embodiment, an enthalpy wheel 360 hasbeen added to the system depicted in FIG. 12a in order to recover energyfrom the exhaust air and improve the overall energy efficiency of thesystem. The performance results of the system are shown in thepsychrometric chart depicted in FIG. 13 b.

EXAMPLES

Due to the ability of the present invention to efficiently producesupply air having a low relative humidity while maintaining a higheroperational cooling coil temperature, it is anticipated that theinvention will be particularly useful in indoor facilities employingfreezing, cooling or refrigeration loads. Such facilities presentsignificant dehumidification challenges due to the combination of alower ambient temperature and a high moisture load. For instance, in anice rink facility, the targeted ambient temperature is 60° F. at 40% RH(relative humidity), which equates to a 35° F. dew point. A moistureload is supplied by forced outdoor air ventilation, uncontrolled outdoorair infiltration, the occupants of the facility, evaporating floodwaterduring ice resurfacing, and the combustion driven ice resurfacer. If therelative humidity within the ice rink facility is not properlymaintained, a fog will develop at the ice surface and condensation willform inside the building as well as on the ice sheet. Additionally, highhumidity will cause an increased load on the ice refrigeration systemresulting in higher energy costs than necessary. Therefore, it iscritical that ice rink facilities utilize a dehumidification systemcapable of creating and maintaining a low humidity environment. As shownin the following examples, it is believed that significant efficiencieswill be realized when a dehumidification system embodying the principlesof the present invention is utilized as an alternative or supplement tomechanical refrigeration systems in low dew point environments such asice rink facilities, operating rooms, supermarkets, and the like.

Example 1

Referring to the psychometric chart depicted in FIG. 5b , an example ofthe performance of the dehumidification system depicted in FIG. 5a isshown. In this example, the system 100 is utilizing a 7.5 toncompressor, a WSG high performance silica gel desiccant wheel rotatingat 7 revolutions per hour, and a 5 HP supply fan. Summer operations arepresumed with a 95° F. outdoor temperature. The hypothetical conditionedspace is in an ice rink facility, where the targeted ambient temperatureis 60° F. at 40% RH (relative humidity), which equates to a 35° F. dewpoint.

Referring to both FIGS. 5a and 5b , first and second air streams 101,102 having dry-bulb temperatures of 55° F. and moisture contents of 32grains/lb (Points A and D′, respectively) are drawn into the bypass andcycle passageways 170, 180 by the air supplier 150. The second airstream 102 enters the inlet 181 of the cycle passageway 180 and isheated to 106.2° F. and 9.34% RH (Point B) by the condenser 210. Thesecond air stream 102 is then cooled and humidified to 71.2° F. and63.56% RH (Point C) as the air passes through the regeneration inlet 125and regenerates the wheel 121. Next, the second air stream 102 passesthrough the cooling coil 230 where it is cooled to its dew point toremove moisture via condensation. Leaving the cooling coil 230, thesecond air stream 102 is at 45.3° F. and 99.96% RH with a dew point of45.29° F. (Point D). Next, the first air stream 101 is heated anddehumidified to 72.9° F. and 13.38% RH with a 21.24° F. dew point (PointE′) as it passes through the exposed portion of the desiccant wheel 121at the first process inlet 127, while the cooled, saturated second airstream 102 is heated and dehumidified to 62.9° F. and 23.81% RH with a26.14° F. dew point (Point E) as it passes through the exposed portionof the desiccant wheel 121 at the second process inlet 129. Thedehumidified first and second air streams 101, 102 are then mixed in thesupply passageway 190 (Point F, 67.9° F. and 17.94% RH) before exitingthe outlet 191 at 70.8° F. and 16.24% RH with a dew point of 23.82° F.(Point G). Under these parameters, the power consumption of the systemis 0.25 Kwh/lb of water removed, with a total moisture extraction of35.7 lb/hr by the system.

Example 2

Referring to the psychometric chart depicted in FIG. 12b , an example ofthe performance of the dehumidification system depicted in FIG. 12a isshown. This system is configured to process both return air and outsideair. In this example, the system 100 is utilizing a 7.5 ton compressor240, a 17 ton compressor 340, a WSG high performance silica geldesiccant wheel rotating at 7 revolutions per hour, and a 5 HP supplyfan. Summer operations are presumed with a 95° F. outdoor temperature.The hypothetical conditioned space is in an ice rink facility, where thetargeted ambient temperature is 60° F. at 40% RH (relative humidity),which equates to a 35° F. dew point.

Referring to both FIGS. 12a and 12b , the first air stream 101consisting of outdoor air has a dry-bulb temperature of 86° F. and amoisture content of 130.0 grains/lb (Point F). The second air stream 102consisting of return air has a dry-bulb temperature of 55° F. andmoisture content of 32 grains/lb (Point A). The first and second airstreams 101, 102 are drawn into the bypass and cycle passageways 170,180 by the air supplier 150.

The first air stream 101 enters the inlet 171 of the bypass passageway170 and passes through the cooling coil 330 to lower the enthalpy of theoutside air before processing it through the desiccant wheel 121.Leaving the cooling coil 330, the first air stream 101 is at 45.0° F.and 99.54% RH with a dew point of 44.88° F. (Point G).

The second air stream 102 enters the inlet 181 of the cycle passageway180 and is heated to 106.2° F. and 9.34% RH (Point B) by the condenser210. The second air stream 102 is then cooled and humidified to 65.2° F.and 86.46% RH (Point C) as the air passes through the regeneration inlet125 and regenerates the wheel 121. Next, the second air stream 102passes through the cooling coil 230 where it is cooled to its dew pointto remove moisture via condensation. Leaving the cooling coil 230, thesecond air stream 102 is at 47.0° F. and 99.52% RH with a dew point of46.87° F. (Point D).

Next, the first air stream 101 is heated and dehumidified to 70.9° F.and 17.16% RH with a 25.07° F. dew point (Point H) as it passes throughthe exposed portion of the desiccant wheel 121 at the first processinlet 127, while the second air stream 102 is heated and dehumidified to62.7° F. and 29.05% RH with a 30.28° F. dew point (Point E) as it passesthrough the exposed portion of the desiccant wheel 121 at the secondprocess inlet 129. The dehumidified first and second air streams 101,102 are then mixed in the supply passageway 190. At Point I, the supplyair stream is at 66.8° F. and 23.03% RH) with a dew point of 28.35° F.Under these parameters, the power consumption of the system is 0.16Kwh/lb of water removed, with a total moisture extraction of 150.7 lb/hrby the system 300.

Example 3

Referring to the psychometric chart depicted in FIG. 13b , an example ofthe performance of the dehumidification system depicted in FIG. 13a isshown. This particular system features an enthalpy wheel 360 in order torecover energy from the exhaust air and improve the overall energyefficiency of the system. In this example, the system 100 is utilizing a7.5 ton compressor 240, a 4 ton compressor 340, a WSG high performancesilica gel desiccant wheel rotating at 7 revolutions per hour, and a 5HP supply fan. Summer operations are presumed with a 95° F. outdoortemperature. The hypothetical conditioned space is in an ice rinkfacility, where the targeted ambient temperature is 60° F. at 40% RH(relative humidity), which equates to a 35° F. dew point.

Referring to both FIGS. 13a and 13b , the first air stream 101consisting of outdoor air has a dry-bulb temperature of 86° F. and amoisture content of 130.0 grains/lb (Point F). The second air stream 102consisting of return air has a dry-bulb temperature of 55° F. andmoisture content of 32 grains/lb (Point A). The third air stream 401consists of return air having a dry-bulb temperature of 55° F. andmoisture content of 32 grains/lb (Point L).

The third air stream 401 enters the exhaust passageway 420 and passesthrough the enthalpy wheel 360, absorbing energy. At Point M, the thirdair stream 401 has a dry-bulb temperature of 80.1° F. and moisturecontent of 108 grains/lb (69.88% RH).

The first and second air streams 101, 102 are drawn into the bypass andcycle passageways 170, 180 by the air supplier 150. The first air stream101 enters the inlet 171 of the bypass passageway 170 and passes throughthe enthalpy wheel 360 and the cooling coil 330 to lower the enthalpy ofthe air before processing it through the desiccant wheel 121. Leavingthe enthalpy wheel 360, the first air stream 101 is at 60.4° F. and69.26% RH with a dew point of 50.3° F. (Point G). Leaving the coolingcoil 330, the first air stream 101 is at 45.0° F. and 99.54% RH with adew point of 44.88° F. (Point H).

The second air stream 102 enters the inlet 181 of the cycle passageway180 and is heated to 106.2° F. and 9.34% RH (Point B) by the condenser210. The second air stream 102 is then cooled and humidified to 65.2° F.and 86.46% RH (Point C) as the air passes through the regeneration inlet125 and regenerates the wheel 121. Next, the second air stream 102passes through the cooling coil 230 where it is cooled to its dew pointto remove moisture via condensation. Leaving the cooling coil 230, thesecond air stream 102 is at 47.0° F. and 99.52% RH with a dew point of46.87° F. (Point D).

Next, the first air stream 101 is heated and dehumidified to 70.9° F.and 17.16% RH with a 25.07° F. dew point (Point I) as it passes throughthe exposed portion of the desiccant wheel 121 at the first processinlet 127, while the second air stream 102 is heated and dehumidified to62.7° F. and 29.05% RH with a 30.28° F. dew point (Point E) as it passesthrough the exposed portion of the desiccant wheel 121 at the secondprocess inlet 129. The dehumidified first and second air streams 101,102 are then mixed in the supply passageway 190 before exiting theoutlet 191 at 66.8° F. and 23.03% RH with a dew point of 28.35° F.(Point K). Under these parameters, the power consumption of the systemis 0.07 Kwh/lb of water removed, with a total moisture extraction of183.6 lb/hr by the system 400.

Example 4

Another alternative embodiment of the dehumidification system of thepresent invention is shown schematically in FIG. 14. The air conditionsystem 100 shown in FIG. 14 is similar to the system shown in FIG. 5a ,except that a damper 177 has been installed in the bypass passageway170. When the damper 177 is in the open position, a freshly regeneratedsection of the desiccant wheel 121 can be rotated sequentially throughthe first and second air streams 101, 102 to optimize desiccant moistureadsorption at the process side of the desiccant wheel. The performanceof the dehumidification system 100 with the damper 177 in the openposition is shown in Table 1. The performance of the dehumidificationsystem 100 with the damper 177 in the closed position is shown in Table2. Under these testing parameters, the efficiency (Kwh/lb H₂O) of thedehumidification system 100 increased by 12.5% when the damper 177 wasin the open position.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art having the benefit ofthe teaching presented in the foregoing description and associateddrawings. Therefore, it is to be understood that the inventions are notto be limited to the specific embodiments disclosed and thatmodifications and other embodiments are intended to be included withinthe scope of the appended claims. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation.

What is claimed is:
 1. A method of conditioning air within an indoorspace using a desiccant dehumidification system, the method comprising:a. conveying a first air stream sequentially through a bypass plenum,through a first process section of a desiccant wheel, through a supplyplenum, and into a conditioned space; b. conveying a second air streamsequentially through a heating plenum, through a regeneration section ofthe desiccant wheel to form a freshly regenerated portion of thedesiccant wheel, through a cooling plenum, through a second processsection of the desiccant wheel, through the supply plenum, and into theconditioned space; c. heating the second air stream as the second airstream passes through the heating plenum; d. cooling the second airstream as the second air stream passes through the cooling plenum; e.rotating the desiccant wheel in a first direction such that the freshlyregenerated portion of the desiccant wheel comes into contact with thefirst air stream leaving the bypass plenum before rotating into contactwith the second air stream leaving the cooling plenum.
 2. The method ofclaim 1, further comprising the steps of: i) releasing moisture from thedesiccant wheel into the second air stream as the second air streammoves from the heating plenum to the cooling plenum; ii) adsorbingmoisture from the first air stream onto the desiccant wheel as the firstair stream moves from the bypass plenum to the supply plenum; and iii)adsorbing moisture from the second air stream onto the desiccant wheelas the second air stream moves from the cooling plenum to the supplyplenum.
 3. The method of claim 2, wherein the second air stream isheated within the heating plenum by a heating means.
 4. The method ofclaim 3, wherein the second air stream is cooled within the coolingplenum by a cooling means.
 5. The method of claim 4, wherein the heatingmeans is a condenser and the cooling means is an evaporator coil.
 6. Themethod of claim 5, wherein the first and second air streams comprisereturn air from the indoor space.
 7. The method of claim 2, wherein thefirst air stream comprises outdoor air and the second air streamcomprise return air from the indoor space.
 8. The method of claim 7,further comprising the step of cooling the first air stream beforetransmitting the first air stream through the first process section ofthe desiccant wheel.
 9. The method of claim 8, further comprising thesteps of transmitting the first air stream through a first side of anenthalpy wheel before cooling the first air stream.